1. Field of the Invention
This invention relates to means for obtaining a sample of molten metal from a heat of the molten metal, and more particularly to a novel apparatus for obtaining a solidified sample of metal from a heat of the molten metal.
2. Description of the Prior Art
In the production and refinement of metals, the numerous variables encountered make it necessary to obtain samples of the metal for constituent analysis at various stages during the refining process. For example, in the production of steel in a basic oxygen furnace, in order to assure the desired composition of the final product, it is necessary to obtain one or more solidified samples from the molten metal in the furnace, and the ladle after tap, immediately analyze the sample and utilize the results of this analysis for determining further processing such as the length of time of any further blowing required, or amount of deoxidant required to "kill" the steel in the ladle or further in the process. One important element of the analysis is the amount of oxygen in the melt at the time of taking the sample and, to obtain this information, the sample is normally "killed" by a small quantity of an oxygen-fixing agent such as aluminum or titanium which is placed in the sample mold cavity and melted by the liquid steel which forms the sample. The oxygen in the sample then combines with the fixing agent to form stable compounds which are retained in the sample and may be detected and mesured during the subsequent analysis.
Numerous devices have been developed in the past for obtaining solidified samples from a melt of steel, which samples are frequently in the form of elongated cylindrical pins or relatively flat cylindrical discs. Sampling devices and procedures have been developed for simultaneously obtaining both a pin-type and a disc-type sample, one such apparatus being disclosed in U.S. Pat. No. 3,915,014 assigned to the assignee of this invention. In such an apparatus, the test sample, generally referred to as a lollipop sample, is obtained by immersing the end of a mold structure into a heat of the metal. The molten metal flows either by ferrostatic pressure alone or in combination with the application of suction into the lollipop-shaped mold cavity, with the handle of the lollipop forming the pin sample and the body of the lollipop forming the disc sample. Other examples of prior art sampling devices include U.S. Pat. No. 3,656,350 which employs a pair of metal cup-shaped elements defining a tortuous path for the molten steel and the oxygen-fixing agent to follow before entering the sample mold cavity, and U.S. Pat. No. 3,704,621 which discloses a dipper-type sampling device having a sample chamber containing a quantity of an oxygen-fixing agent and closed by a closure which is destroyed by the heat of the steel.
While the known prior art sampling devices have met with varying degrees of approval and success, the ever-increasing demands on the steel industry for strict product quality control places even greater emphasis on the necessity for obtaining reliable test samples. One difficulty which has been encountered with the prior art sampling devices is the fact that the oxygen-fixing agent normally placed within the mold chamber (or in the case of, for example, U.S. Pat. No. 3,656,350, in one of the metal cups to which the molten steel must flow in its path into the sample mold cavity) has not been uniformly dispersed through the metal of the sample. As a result, the steel sample was not always thoroughly killed so that an accurate oxygen content was not always reflected upon analysis of the sample.
Another difficulty encountered in obtaining suitable samples in the past has been the entry of impurities into the sample mold from the layer of slag or casting powder normally covering the heat of molten steel.
It is therefore a primary object of the present invention to provide an improved molten metal sampling apparatus which will enable a more accurate and reliable analysis of the metal sample.